Process for increasing the frictional resistance between threads, yarns and the like of synthetic linear polyamides and product made thereby



ifilfifld Patented Jan. 30, 1952 flee 3,019,132 PROCES FDR INCREASENG THE FRICTIQNAL RESISTANCE BETWEEN THREADS, YARNS AND THE LIKE F SYNTHETIC LINEAR POLY- AMIDES AND PRODUCT MADE THEREBY Rudolf Gables, Tamins, Switzerland, assignor to l nventa AG. fiir Forschung and Patentverwertung, Lueerne, Switzerland N0 Drawing. Filed Jan. 16, 1957, Ser. No. 634,420 Claims priority, application Switzerland Jan. 21, 1956 11 Claims. (Ci. 117-4383) The present invention relates to a process for increasing the frictional resistance between elements, such as threads, yarns and the like of synthetic linear polyamides and to the product made by this process.

Synthetic fibres made from synthetic linear polyamides have an absolutely smooth surface when they are of circular cross-section. They, therefore, differ fundamentally from natural fibres such as wool, cotton, silk etc. which have a rough scaly surface structure.

The small specific surface area and the smoothness of polyamide fibres has the great disadvantage that these fibres adhere to one another very slightly and are easily relatively displaced when assembled together and easily become separated in fabrics made of mixed fibres. Also, in the case of fabrics in which the warp and weft threads consist of synthetic yarns, there is a pronounced tendency to relative displacement which may lead to streakiness in the fabric. A further consequence of the lack of frictional resistance between the fibres, is that, when nets are made of synthetic fibres, the knots do not hold and rapidly open or become loose during use.

Attempts have been made for a long time to obviate the disadvantage of the small adherence of synthetic fibres by providing them with a suitable dressing. The processes previously proposed were concerned mainly with the semi-synthetic fibres of the rayon group, but could also be applied with more or less successful results to fully synthetic fibres.

The methods which have previously been proposed for increasing the resistance to slipping can be divided into two main groups.

The processes of the first group consist in impregnation with resin, for which purpose natural resins, but for the most part artificial resins, have been proposed. (Resin acids of colophony in French Patent No. 841,487, Rubber in Italian Patent No. 388,046, Phenol and thiourea resins in Swiss Patents Nos. 233,338-233,342, Urea Resins in German Patent No. 717,093, Melamine resins in US. Patent No. 2,491,454 and Polyvinyl chloride in British Patent No. 612,227.) The second group comprises those processes in which a certain amount of roughness is imported to the fibres by superficial application of fine-grained mineral substances. (Silicic acid in US. Patents Nos. 2,375,738, 2,696,444 and Swiss Patent No. 299,340, Silicates in German Patent No. 737,152.)

The method of increasing the resistance to slipping by application of a resin dressing has the disadvantage that the nature of the fibres is altered by the impregnation and this in many cases is undesirable. Thus, for example, most of the artificial resin dressings which are applied affect the stiffness of the fibres or yarns; others af- 2 feet their swelling properties, their elasticity, electrostatic behaviour etc. to an undesirable extent.

In the process of the second group in which the frictional resistance is increased purely mechanically by means of superficially applied powder dispersions, the nature of the fibre is, to a large extent, maintained. Also, these processes have the advantage that they are very effective even when small amounts are applied. On the other hand, the adherence of silicic acid or silicate particles to the surface of the fibres is unsatisfactory. Whereas in the case of cellulose fibres having a wrinkled surface, a tolerable adherence of a silicic acid dressing can be obtained, its adherence to circular polyamide fibres produced by melt spinning is so slight that the greater part of the silicic acid is removed during the spinning or weaving or during the knotting of nets.

According to the present invention, the frictional resistance between fibres or threads of synthetic linear polyamides is greatly improved by treating them with a dispersion of a fine-grained polyamide powder in a polyamide adhesive. The adhesive may be in fine liquid dispersion as in the form of a solution or emulsion.

All thread-like structures made from any known types of polyamide are suitable for treatment by the process of the invention, for example, those of polycaprolactam, polyhexamethylenediammoniumadipate and poly w aminoundecanoic acid. The filament or thread-like structure can be in the form of twisted or untwisted endless yarns or monofils or cup staple.

The polyamide powder which is to be adhered to the fibres can consist of the same material as the fibres. It is advantageous however, .to use those polyamides which have high swelling properties such as, for example, po1ycaprolactam or mixed polyamides consisting of two or three different polyamide-forming components.

The manufacture of the polyamide powder takes place in the usual manner by cutting fine-fibred yarn waste or by grinding granular material in a colloid mill. Very fine powder can be made by a wet method in accordance with US. Patent No. 2,639,278 by dissolving the polyamide in a suitable solvent and recovering it in a finegrained form by cooling. From the crude powder obtained fractions of uniform grain size down to below l,u (micron) diameter can be obtained by screening or with an air separator. The powders used in the method of the invention have, in general, a grain size, which is smaller than 40 and which is small relative to the diameter of the thread-like structure to be treated; preferably it is less than one-tenth of the thickness of the thread.

The powder is suspended in a solution or emulsion of a suitable polyamide adhesive and protective colloid or wetting agent may be added for the purpose of stabilizing the suspension. As the protective colloid, non-ionogenous condensation products of ethylene oxide are suitable. Practically all known polyamide adhesive agents can be used for fixing the powder to the surface of the thread-like structure. These are, for example, the alcohol-soluble mixed polyamides. soluble polyamides on the basis of dilinoleic acid and diamines, the methylol and alkoxymethyl polyamides modified by formaldehyde and thereby made soluble, phenol-formaldehyde resins in their resolution stage, polyisocyanate adhesives, combinations of resorcinol or pyrocatechol with aldehydes, for

example propionic aldehyde solution, polyvinyl acetate and various polyvinyl acetals such as polyvinylformal and polyvinyl butyral, amongst others. The method by which the process of the invention is carried out depends to a large extent on the kind of fibrous material to be treated. Endless yarns and thin monofils up to about 300 denier can be treated on the usual single thread dressing machines, in which the threads are passed over rollers wetted with the powder dispersion. The drying of the treated yarn preferably takes place directly on the bobbin of the dressing machine at a temperature of 20- 50 C. However, a heating chamber may adjoin the dressing machine and the dressed yarn can be dried either before or while it is running on to the bobbin. Coarse twisted yarns and monofils of more than 300 denier are passed continuously through a bath containing the powder dispersion and then through a heating pipe or heating chamber, several metres in length, in which the solvent or the liquid of the dispersion is evaporated. When the adhesive used is a duroplast, for example, on the basis of phenols and aldehydes, the drying process is preferably carried out in such a way that hardening of the adhesive already takes place in the heating zone.

In the case of staple fibres, another procedure can be adopted in order to prevent the individual fibres from sticking together. This can be avoided, for example, by making the polyamide powder into a paste or causing it to swell up with the liquid or dissolved adhesive and then dispersing it in a liquid which does not dissolve either the adhesive or the polyamide fibre. In this way, the adhesive becomes effective only at the places where the polyamide grains are in contact with the surface of the fibres. The fibres are sprayed with the dispersion or are dipped into it and then squeezed and dried. If the fibres stick to one another to some extent they can easily be separated by fibre-opening devices of the usual kind.

The method of the invention results in the production of polyamide fibres, threads, yarns and monofilshaving a durable roughened surface. It is particularly to be noted that the inter fibre friction is increased but the cofefiicient of friction on bright metal surfaces is reduced. This will now be explained with the aid of some numerical examples.

Untreated threads of poly-e-caprolactam have a coefficient of friction of 0.30.35 on polished steel. The coefiicient of friction of thread to tthread, on the other hand, is only 0.14-0.16, which explains the small resistance to slipping of the untreated yarn.

When treated with a powder dispersion in accordance with the invention, the same threads have a coefiicient of friction to steel of 01-015 and of thread to thread of 0.250.5. The treated material, therefore, has a distinctly increased resistance to relative slipping of the threads but slides more easily over smooth surfaces, rods, thread guides, eyes and the like made of steel, ceramic materials or other substances which is very desirable in the further treatment process.

The invention will now be explained with the aid of the following samples but it is not limited thereto.

Example 1 A stretched yarn of poly-e-caprolactam made up of 40 threads with a total titre of 240 denier is drawn off from a conical bobbin, passed through a tensiouing device by which the thread tension is adjusted to 20 g., and guided tangentially along a dressing roller which dips into the dressing liquid and is finally wound on a cylindrical perforated aluminium bobbin. The yarn is drawn off at a speed of l120 metres per minute during the dressing. The dressing liquid consists of 5% solution of a polyamide made from dilinoleic acid and ethylene diamine in a toluene-isopropanol mixture in which are suspended of a powder of poly-e-caprolactam of an average grain size of 511..

The treated yarn is dried by allowing it to stand for 48 hours at 40 C. and 45% relative humidity and then has a durable dressing of 3.5% of the original weight of the yarn. The coefiicient of friction of the yarn on bright steel amounts to 0.135 as compared with its previous coefficient of 0.312 and a coefficient of friction of thread to thread of 0.274 as compared with its previous coefficient of 0.128.

Example 2 A twisted yarn of caprolactam polyamide of a total titre of 2,200 denier and a structure of 250/40 8-32-38 is drawn off at a speed of 10 metres per minute from a bobbin and passed through a tension regulating device which gives it a pre-tension of 0.81.0 kg. The yarn is then guided by means of two deflecting rollers through a treatment bath and then through a tube which is two metres in length and heated to 300 C., after which it is wound on a drum.

The treatment bath contains a 10% aqueous emulsion of polyvinyl acetate in which are dispersed 15% of a powder of poly-ecaprolactam having an average grain size of 30 The treated yarn contains 5% of a rough dressing which adheres well to it and has a coefficient of friction of 0.420 (thread to thread) as compared with a coefficient of 0.136 in the untreated condition.

Example 3 A monofil of polyhexamethylenediammoniumadipate of 1.2 mm. diameter is treated with a powder dispersion in an apparatus similar to that used in Example 2 at a speed of 14.5 metres per minute and a pre-tension of 2.65 kg., and then dried and reeled. The treatment liquid consists of an 8% methanol solution of a resorcinol-propionic aldehyde adhesive in which 13.5% of a powdered mixed polyamide consisting of 60 parts of hexamethylenediammoniumadipate and 40 parts of caprolactam with an average grain size of 30,11. are suspended.

The treated monofil has a 6.5% layer which imparts to it a good resistance to slipping. The coefficient of friction of monofil to monofil amounts to 0.285 as compared with the previous coefficient of 0.118.

What is claimed is:

1. A process for increasing the frictional resistance between filaments of a synthetic linear polyamide which comprises treating the filaments with a dispersion of a fine-grained powder composed of said polyamide and in solid particle form in fine liquid dispersion in an organic polyamide-binding adhesive and drying the filaments to bond said powder in solid particle form on said filaments to roughen thereby the surfaces of said filaments.

2. A process as in claim 1 wherein said polyamide is poly-epsilon-caprolactam.

3. A process according to claim 1, in which the polyamide powder to prevent frictional resistance between the filaments has a grain size smaller than 40g.

4. A process according to claim 1, in which a solution of a polyamide of dilinoleic acid and ethylenediamine is used as adhesive.

5. A process according to claim 1, in which polyvinyl acetate in fine liquid dispersion is used as adhesive.

6. A synthetic linear polyamide filament having a coating in the form of a powder composed of the same polyamide and bonded to the surface of said filament in solid particle form by adhesive to render the surface discontinuous and rough and to increase thereby frictional resistance between filaments.

7. A synthetic linear polyamide filament according to claim 6, in which the synthetic linear polyamide is of the class consisting of poly-e-caprolactam, polyhexamethylenediammoniumadipate, and poly-w-aminoundecanoic acid.

8. A synthetic linear polyamide filament according to claim 6, in which the polyamide powder to prevent frictional resistance between the filaments has a grain size smaller than 40 10. A synthetic linear polyamide filament according to claim 6, in which the adhesive is a solution of a poly-Q amide of dilinoleic acid and ethylenediamine.

11. A synthetic linear polyamide filament according tq claim 6, in which the adhesive is polyvinyl acetate.

2,443,450 Graham et a1 June 15, 1948 6 Taylor Apr. 22, 1952 Lowell Dec. 30, 1952 Stott et al. May 19, 1953 Watson et al. July 26, 1955 Toulmin Jan. 17, 1956 Horn et a1. May 22, 1956 Murdock Dec. 22, 1959 FOREIGN PATENTS Great Britain Oct. 14, 1949 Australia May 17, 1951 Great Britain Sept. 3, 1952 France July 22, 1955 

1. A PROCESS FOR INCREASING THE FRICTIONAL RESISTANCE BETWEEN FILAMENTS OF A SYNETHETIC LINEAR POLYAMIDE WHICH COMPRISES TREATING THE FILAMENTS WITH A DISPERSION OF A FINE-GRAINED POWDER COMPOSED OF SAID POLYAMIDE AND IN SOLID PARTICLE FORM IN FINE LIQUID DISPERSION IN AN ORGANIC POLYAMIDE-BINDING ADHESIVE AND DRYING THE FILAMENTS TO BOND SAID POWDER IN SOLID PARTICLE FORM ON SAID FILAMENTS TO ROUGHEN THEREBY THE SURFACES PF SAID FILAMENTS. 